The present invention relates to a method for operating an internal combustion engine, having at least one catalytic converter, and thereby for assuring that a sufficient quantity of reducing agent is supplied for the operation of the SCR catalytic converter.
The operation of motor vehicles with internal combustion engines is performed in conjunction with the discharge of toxic emissions. Different measures have already been taken to reduce emissions injurious to health and the environment. The so-called SCR catalytic converter (Selective Catalytic Reduction), which in the presence of a reducing agent reduces the nitrogen oxides contained in the exhaust gas to nitrogen, was, for example, developed to reduce the nitrogen oxides contained in the exhaust gas. During the course of the reaction, ammonia, which is mixed into the exhaust gas, is required. In order to provide the ammonia, a diluted urea solution is employed as a rule, which is injected into the exhaust gas tract upstream from SCR catalytic converter with the aid of a metering unit. The maintenance of this diluted urea solution takes place in a separate reducing agent tank.
For environmental reasons and also on account of governmental regulations, provision must be made for a sufficient quantity of a reducing agent to be present for a proper exhaust gas after-treatment. For this reason, reducing agent tanks with fill level sensors are already known so that the fill level of the reducing agent tank can be displayed; and if need be a filling of the tank with the appropriate reducing agent can be performed at a filling station, respectively a gas station. It is in this case, however, problematic that the driver of the motor vehicle is as a rule not capable of determining to what extent the remaining quantity of reducing agent is sufficient to reach a certain destination and in particular a certain filling station. Furthermore, the driver of the motor vehicle is as a rule not sufficiently informed as to where appropriate filling stations, respectively gas stations, are located, which offer the reducing agent, for example the so-called AdBlue. This can consequently lead to all of the reducing agent in the reducing agent tank being consumed before a filling station has been duly located. In so doing, the operating agent for the SCR catalytic converter is lacking so that a proper exhaust gas after-treatment can no longer take place. As the case may be, the driver of the motor vehicle may be made aware of the situation by means of a fill level indicator for the reducing agent tank. Because the operation of the motor vehicle is, however, nevertheless still possible, the driver may possibly not pay proper attention to the indicator.
With regard to the fuel of a motor vehicle, different approaches already exist for avoiding an unintended emptying of the fuel tank. The German patent application DE 101 05 175 A1 accordingly describes a motor vehicle computer system with a sending unit, a receiving unit and a selection device, wherein the current location data of the motor vehicle are transmitted to a provider when a specified threshold of the tank contents is undershot. Location data and gasoline price data from gas stations, which are located within a predetermined distance to the current position of the motor vehicle, are thereupon received. The German patent application DE 101 46 789 A1 describes a comparable method, wherein the maximum cruising range of the motor vehicle is calculated using a measurement of the quantity of fuel contained in the fuel tank. A routing to a gas station within the cruising range is then performed by a navigation system.
These systems therefore offer the possibility of avoiding an unintended emptying of the fuel tank by punctually directing the driver of the motor vehicle to a gas station via a navigation system. However, an unintended emptying of the reducing agent tank, which supplies the operating means for an SCR catalytic converter, cannot hereby be avoided.
The task underlying the invention is therefore to provide a method and a device, which make it possible to avoid an unintended emptying of the reducing agent tank.
This task is solved by a method and an arrangement for operating an internal combustion engine, as they are described in the independent claims. Preferred configurations, respectively embodiments, thereof are described in the dependent claims.